What is the best way to keep external links up to date?

[deoren]

While reviewing some recent doc changes (#593), I noticed a higher than usual number of external links from the output module doc page to external documentation sources for the product that the module would be used with. Providing those references makes perfect sense to me, but I wonder whether we're better served by including the references in-line or if we should use substitution references instead.

If the latter, we would theoretically have one file to parse periodically with a script to determine if links need to be fixed. If the former, we'll need to rely entirely on sphinx-build to validate links for us. In the end, that may be sufficient.

Just noting my thoughts here as an issue for further discussion while I had a moment to do so.